Workers Compensation Assets and Liabilities - Summary of Workers' Compensation Loss Reserve Activity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Liability for Unpaid Claims and Claims Adjustment Expense
Total loss reserves, beginning of period	$ 254,614	$ 190,102
Incurred
Current year	26,936	22,774
Prior years	601	5,263
Total incurred	27,537	28,037
Paid
Current year	(260)	(711)
Prior years	(21,583)	(17,276)
Total paid	(21,843)	(17,987)
Total loss reserves, end of period	$ 260,308	$ 200,152